T. vaginalis Resists Standard Metronidazole Dosage

OB/GYN News, July 15, 2000 by Barbara Baker

SAN FRANCISCO -- About 2%-5% of Trichomonas vaginalis isolates are currently resistant to standard metronidazole treatment, Dr. George Schmid said at the annual meeting of the International Infectious Disease Society for Obstetrics and Gynecology, USA.

The problem is widespread throughout the United States and probably the world. Those who fail treatment usually respond only to more intensive treatment with metronidazole, said Dr. Schmid of the division of STD prevention at the Centers for Disease Control and Prevention, Atlanta.

The standard treatment of T. vaginalis is a single 2-g oral dose. An alternative is 500 mg twice a day for 7 days.

Patients who fail standard treatment are best given 2 g of metronidazole a day for 3-5 days. Tinidazole, which is not marketed in the U.S., is more effective than metronidazole and can be obtained through compounding pharmacies he said.

The CDC, the referral site for patients who fail standard treatment for T. vaginalis infection, collected 195 isolates from 38 states between 1985 and 1998; 91% were resistant to standard doses of metronidazole. Patients were treated with high-dose metronidazole and occasionally tinidazole.

Of 82 resistant cases with a known treatment outcome, 65 were cured.

The CDC also evaluated 911 consecutive women attending a gynecologic clinic. They found that 82 women (9%) had vaginal secretions positive for T. vaginalis. Among those isolates, two (2.4%) were resistant to metronidazole. Twenty-six of the women returned for reculture 1 week after treatment with 2 g of metronidazole; all were cured, Dr. Schmid said.